IGE AND MAST CELLS
IgE molecules are just as specific for their antigen as other antibody isotypes but they operate in a rather different way. Their main function is to defend the body against parasites such as ringworms and flukes – these are much larger than bacteria and viruses so the body has different strategies for killing them. In the tropics, where parasites are common, quite high levels of IgE may be found even in non-allergic people. Cooler conditions are not as favourable to parasites and they are far less of a health problem – in non-allergic people living in temperate climates, the level of IgE is usually very low.
Like other antibodies, IgE molecules are produced by B cells. But once they have been produced, the IgE molecules behave difference from most other antibodies in that they attach themselves to mast cells and basophils. These two types of cell look slightly different under the microscope, and whereas basophils are found floating in the blood, mast cells are embedded in the solid tissues of the body. Mast cells are better known and understood, so we will conveniently ignore the basophils from here onwards: the two types of cell probably work in much the same way.
Although the stem of the IgE molecule is attached to the mast cell, the antigen-binding sites are still free. So when the right, antigen comes along, it will bind to the IgE molecules. This is the signal the mast cell has been waiting for. Packets of chemicals inside the cell are suddenly released to the outside, where they act as messengers, causing major changes in the cells and tissues around them.
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